The present invention resides in the field of discrete particle manufacture, and particularly is concerned with the problem of repeatably forming particles having virtually identical size and shape.
The granules or particles manufactured by the present invention have utility in numerous fields including gripping elements for road surfaces and abrasive grains for use in bonded abrasive articles such as grinding wheels and snagging wheels, and coated abrasive articles such as abrasive papers and the like. One of the problems that has plagued the industry in the manufacture of discrete particles for use as abrasive grains has been the inability to continually reproduce grains of the same size and shape. That is, it has been customary in the past to manufacture abrasive grains by crushing abrasive type material into granular form. However, in the case of heavy duty abrasive grits, usually less than 50% of the total material is recovered in a usable size range, with the majority of the material being crushed into useless fines. Further, that material which is usable must then be classified into standard grain sizes. However, since the crushing process cannot be accurately controlled, the shape of the grains even within a particular classification will vary materially, thus producing grains with dissimilar cutting rates and variable useful lives, thereby resulting in less than optimal efficiencies. The shape of crushed abrasive particles can be improved somewhat by mulling, however such process is not only costly but results in even lower recoveries.
U.S. Pat. No. 3,481,723 illustrates a method of producing shaped abrasive grains by extruding predetermined lengths of a green ceramic mixture which is then sintered to form hard abrasive grains. However, due to the extrusion forming thereof, the shape of such grains is severely limited to a pre-shaped cylindrical or prismatic configuration, with the only variable cross-section lying in a plane perpendicular to the axis of extrusion. Therefore, although the extruded sintered abrasive grains were an improvement over the randomly crushed grains, they have not been entirely satisfactory since variable 3-dimensional geometric solids are not obtainable and the manufacturing process is not particularly economical.
The present invention not only obviates the problem of repeatably producing uniform particles of virtually identical size and shape, but also provides a simplified continuous or repeatable process for rapidly and economically producing such particles in mass production.